3D object recognition

ABSTRACT

A method, device, system, and computer program for object recognition of a 3D object of a certain object class using a statistical shape model for recovering 3D shapes from a 2D representation of the 3D object and comparing the recovered 3D shape with known 3D to 2D representations of at least one object of the object class.

PRIORITY STATEMENT

This U.S. non-provisional application claims benefit of priority under35 U.S.C. §119 of Swedish Patent Application No. 0402048-3, filed onAug. 19, 2004, and U.S. Provisional Application No. 60/603,266 filed onAug. 23, 2004, the entire contents of both of which are incorporatedherein by reference.

FIELD OF THE INVENTION

The present invention relates to automated object recognition and inparticular to automated object recognition of 3D objects usingstatistical shape information.

BACKGROUND OF THE INVENTION

There exist extremely reliable methods for personal identification usingbiometric data such as e.g. fingerprints, retinal patterns or similarunique features of the subject that rely on the cooperation of thesubject. Face recognition may be an effective way of identifying aperson without the cooperation or knowledge of the person. There are twomain general problems for a face recognition system; identifying aperson, i.e. determine the identity from images, and verifying theidentity of a person, i.e. to certify that the person is who he/sheclaims to be. Specific applications are e.g. immigration, ID-cards,passports, computer logon, intranet security, video surveillance andaccess systems. The present invention aims at increasing the performanceand efficiency of such systems using geometric information availablethrough the use of statistical shape models.

In the area of statistical shape models, the invention is related to theActive Shape Models (ASM), introduced by Cootes and Taylor, ([1]: CootesT. F. and Taylor C. J, Active Shape Model Search using Local Grey-levelModels: A Quantitative Evaluation, British Machine Vision Conference, p.639-648, 1993). One distinction is that ASM have been used for inferring2D shape from 2D observations or 3D shape from 3D observations whereasthe invention uses 2D observations, i.e. images, to infer 3D shape. Alsothe observations are from multiple views (one or more imaging devices),something that is not handled in standard ASM. Cootes and Taylor have anumber of patents in the area, the most relevant are(WO02103618A1—Statistical Model) where parameterisation of 2D or 3Dshapes are treated, (WO0135326A1—Object Class Identification,Verification or Object Image Synthesis) where an object class isidentified in images and (WO02097720A1—Object Identification) in whichobjects are identified using modified versions of ASM and relatedtechniques. Also related is Cootes et al. ([2]: Cootes T. F., Wheeler G.V, Walker K. N and Taylor C. J., View-based Active Appearance Models,Image and Vision Computing, 20(9-10), p. 657-664, 2002.) wheremulti-view models are used but no explicit or consistent 3D data iscontained in the model. There are also methods for deforming a 3D modelof the object to fit the 2D projections of the object in the images suchas in Blanz and Vetter ([3]: Blanz V. and Vetter T., Face RecognitionBased on Fitting a 3D Morphable Model, IEEE Trans. on Pattern Analysisand Machine Intelligence, 25(9), p. 1063-1073, 2003.). These methods arevery computationally expensive and often require manual intervention.Related patents are U.S. Pat. No. 6,556,196/EP1039417 (Method andapparatus for the processing of images) which describes a method formorphing a 3D model so that it will be a 3D representation of the objectin the image by minimizing the projection error in the image.

One common problem for image based recognition is detecting the 2D shapeof the object in the image, i.e. finding the relevant image region.Recent methods for detecting objects in images usually involve scanningthe whole image at different scales for object specific image patternsand then using a classifier to decide if the region is relevant or not.The latest developments suggest the use of Support Vector Machines (SVM)for this task. A key element is the extraction of image features, i.e.parts of the image such as corners, edges and other interest points.This is usually done using correlation based schemes using templates oredge based methods using image gradients. For an overview of methods forface detection and feature extraction, cf. Zhao and Chellappa ([4]: ZhaoW., Chellappa R., Rosenfeld A and Phillips P. J, Face Recognition: ALiterature Survey, Technical report CAR-TR-948, 2000.) and thereferences therein. In [4] a review of current image based methods forface recognition is also presented.

When using image based methods for identification and verification thereare two major problems, illumination variation and pose variation.Illumination variation will affect all correlation based methods whereparts of images are compared since the pixel values vary with changingillumination. Also specular reflections can give rise to high changes inpixel intensity. Pose variation occurs since the projection in the imagecan change dramatically as the object rotates. These two problems havebeen documented in many face recognition systems and are unavoidablewhen the images are acquired in uncontrolled environments. Most of theknown methods fail to handle these problems robustly.

The illumination problem is handled by the invention since no imagecorrelation or comparison of image parts is performed. Instead featuressuch as corners which are robust to intensity changes are computed,which make the shape reconstruction, to a large extent, insensitive toillumination and specular reflections. The invention handles the poseproblem by using any number of images with different pose for trainingthe statistical model. Any subset of the images, as few as a singleimage, can then be used to infer the 3D shape of the object.

SUMMARY OF THE INVENTION

The invention consists of a statistical model of the shape variations ina class of objects relating the two-dimensional (2D) projection inimages to the three-dimensional (3D) shape of the object and the use ofthe 3D shape information for identification or verification of theobject. Furthermore, the present invention relates to an imageprocessing device or system for implementing such a method. The processis fully automatic and may be used e.g. for biometric identificationfrom face images or identification of objects in for instance airportsecurity X-ray images. The recovered 3D shape is the most probable shapeconsistent with the 2D projections, i.e. the images. The statisticalmodel needs a bank of data, denoted training data, where the 3Dpositions of the image features are known, in order to learn theparameters of the model. Such data sampling can be done using e.g.binocular or multi-view stereo or range scanners. Once the modelparameters are learned, the 3D shape can be computed using one orseveral images. The 3D shape is then used, by means of the presentedinvention together with the 2D image data, to identify or verify theobject as a particular instance of the object class, e.g. the facebelonging to a certain individual. A positive (or negative)identification initiate proper action by means of the presentedinnovation.

In a preferred embodiment of the invention, a method for objectrecognition of a three dimensional (3D) object is presented, the methodcomprising the steps of:

-   -   obtaining at least one two dimensional (2D) representation of        the object;    -   detecting image features in the obtained 2D representation;    -   recovering a highly probable 3D shape of the object of a certain        object class consistent with 2D images of the object using at        least one obtained image where 2D features are detected and        using a learned statistical multi-view shape model of the shape        variation; and    -   comparing the recovered 3D shape with a reference representation        of at least one object of the object class.

In the method, the recovered 3D shape may be a complete surface model.

Still in the method, the complete surface model may be inferred from 2Dor 3D features.

In another aspect of the method according to the present invention, theobject class may contain non-rigid objects and the statistical shapemodel may be learned using 2D and 3D data specific for possibledeformations of the objects in the non-rigid object class.

The method may further comprise the step of identifying an individualobject of an object class or aiding in the identification of anindividual object using the recovered 3D shape.

The method may yet further comprise the step of verifying the identityof an individual object of an object class or aiding in the verificationof the identity of an individual object using the recovered 3D shape.

The method may further comprise the step of: fitting a surface to therecovered 3D shape using a learned statistical shape model for thesurface of the object in order to regularize the surface shape in amanner specific for the object class.

In the method the object may be one or several of: a human face, a humanbody, inner organ(s) of a human body, blood vessel, animal, inner organsof an animal, a tumor, manufactured product(s) from an industrialprocess, a vehicle, an aircraft, a ship, military object(s).

In the method the reference representation may be stored in at least oneof a non-volatile memory, database server, and personal identificationcard.

In another embodiment of the present invention, a device for objectrecognition of a three dimensional (3D) object is presented, comprising:

-   -   means for obtaining at least one two dimensional (2D)        representation of the object;    -   means for detecting image features in the obtained 2D        representation;    -   means for recovering a highly probable 3D shape of the object of        a certain object class consistent with 2D images of the object        (607) using one or more images where 2D features are detected        and using a learned statistical multi-view shape model of the        shape variation; and    -   means for comparing the recovered 3D shape with a reference        representation of at least one object of the object class.

In the device the recovered 3D shape may be a complete surface model andthe complete surface model may be inferred from 2D or 3D features.

In the device the object class may contain non-rigid objects and thestatistical shape model may be learned using 2D and 3D data specific forpossible deformations of the objects in the non-rigid object class.

The device may further comprise means for identifying an individualobject of an object class or aiding in the identification of anindividual object using the recovered 3D shape.

The device may still further comprise means for verifying the identityof an individual object of an object class or aiding in the verificationof the identity of an individual object using the recovered 3D shape.

The device may further comprising means for: fitting a surface to therecovered 3D shape using a learned statistical shape model for thesurface of the object in order to regularize the surface shape in amanner specific for the object class.

In the device the object may be one or several of: a human face, a humanbody, inner organ(s) of a human body, blood vessel, animal, inner organsof an animal, a tumor, manufactured product(s) from an industrialprocess, a vehicle, an aircraft, a ship, military object(s).

In the device the recovered 3D shapes of blood vessels or organsrecovered from 2D projections, e.g. using X-ray imaging may be used fornavigating steerable catheters or aiding physicians by displaying therecovered 3D shape.

The recovered 3D shapes of facial features may be used in the device toidentify or to verify an identity of an individual in an access controlsystem or security system, resulting in an acceptance or rejection ofthe individual.

The device may further comprise an interface for communicating with apersonal identification card wherein the reference representation isstored.

Yet another embodiment of the present invention, a computer programstored in a computer readable storage medium and executed in acomputational unit for object recognition of a three dimensional (3D)object is presented, comprising:

-   -   an instruction set for obtaining at least one externally        acquired two dimensional (2D) representation of the object;    -   an instruction set for detecting image features in the obtained        2D representation;    -   an instruction set for recovering a highly probable 3D shape of        the object of a certain object class consistent with 2D images        of the object using one or more images where 2D features are        detected and using a learned statistical multi-view shape model        of the shape variation; and    -   an instruction set for comparing the recovered 3D shape with a        reference representation of at least one object of the object        class.

The computer program may further comprise an instruction set foridentifying and/or verifying an individual object of an object class oraiding in the identification and/or verification of the individualobject using the recovered 3D shape.

In another embodiment of the present invention, a system for objectrecognition of a three dimensional (3D) object is presented, comprising:

-   -   means for obtaining at least one two dimensional (2D)        representation of the object;    -   means for detecting image features in the obtained 2D        representation;    -   means for recovering a highly probable 3D shape of the object of        a certain object class consistent with 2D images of the object        using one or more images where 2D features are detected and        using a learned statistical multi-view shape model of the shape        variation;    -   means for comparing the recovered 3D shape with a reference        representation of at least one object of the object class; and    -   means for responding to a result from the means for comparison.

The system may further comprise means for identifying and/or verifyingan individual object of an object class or aiding in the identificationand/or verification of the individual object using the recovered 3Dshape.

In the system the reference representation may be stored in at least oneof a non-volatile memory, database server, and personal identificationcard.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention will be described in a non-limiting wayand in more detail with reference to exemplary embodiments illustratedin the enclosed drawings, in which:

FIGS. 1 a-1 c illustrate a two-step procedure for recovering 3D datafrom an input image.

FIGS. 2 a-2 c illustrate a process of surface fitting to a recovered 3Dshape.

FIG. 3 is a schematic block diagram of a device according to the presentinvention.

FIG. 4 illustrates a schematic block diagram of the steps of a methodaccording to the present invention.

FIG. 5 is a schematic illustration of a system according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The invention consists of an image processing system for automaticrecovery of 3D shape from images of objects belonging to a certainclass. This 3D reconstruction is done by establishing a statisticalshape model, denoted the feature model, that 3D positions. Such a modelis learned, i.e. the model parameters are estimated, from training datawhere the 2D-3D correspondence is known. This learning phase may be doneusing any appropriate system for obtaining such 2D-3D correspondence,including, but not limited to binocular or multi-view image acquisitionsystems, range scanners or similar setups. In this process the object ofinterest is measured and a reference model of the object is obtainedwhich may be used in subsequent image analysis as will be describedbelow.

Given an input image, the process of recovering the 3D shape is atwo-step procedure. First the image features such as points, curves andcontours are found in the images e.g. using techniques such as e.g. ASM[1] or gradient based methods or classifiers such as SVM. Then the 3Dshape is inferred using the learned feature model. This is illustratedin FIG. 1. FIG. 1 a illustrates an image of a face to be analysed, FIG.1 b illustrates the detection of object features to be used in theanalysis and shape information process, and FIG. 1 c illustrates theinferred 3D shape to be used in the recognition process.

There is also the option of extending the 3D shape representation fromcurves and points to a full surface model by fitting a surface to the 3Ddata. This is illustrated in FIG. 2, where FIG. 2 a illustrates theinferred 3D shape, 2 b illustrates a fitted surface to the 3D data, andFIG. 2 c illustrates a 3D rendered surface model of the fitted surface.

The Feature Model

Suppose we have a number of elements in a d-dimensional vector t, forexample, a collection of 3D points in some normalized coordinate system.The starting point for the derivation of the model is that the elementsin t can be related to some latent vector u of dimension q where therelationship is linear:t=Wu+μ  (1)where W is a matrix of size d×q and μ is a d-vector allowing fornon-zero mean. Once the model parameters W and μ have been learned fromexamples, they are kept fix. However, our measurements take place in theimages, which usually is a non-linear function of the 3D featuresaccording to the projection model for the relevant imaging device.

Denote the projection function with ƒ: R^(d)→R^(e), projecting all 3Dfeatures to 2D image features, for one or more images. Also, we need tochange coordinate system of the 3D features to suit the actualprojection function. Denote this mapping by T: R^(d)→R^(d). Typically, Tis a similarity transformation of the world coordinate system. Thus,f(T(t)) will project all normalised 3D data to all images. Finally, anoise model needs to be specified. We assume that the image measurementsare independent and normally distributed, likewise, the latent variablesare assumed to be Gaussian with unit variance u˜N(0,I). Thus, insummary:t _(2D)=ƒ(T ₍ t))+ε=ƒ(T(Wu+μ))+ε  (2)where ε˜N(0, σ² I) for some scalar σ. The model is related to PPCA, cf.Tipping and Bishop ([5]: Tipping M. E., Bishop C. M., ProbabilisticPrincipal Component Analysis, Phil. Trans. Royal Soc. London B, 61(3),p. 611-622, 1999.), but there are also differences due to thenon-linearity of f(.). Before the model can be used, its parameters needto be estimated from training data. Given that it is a probabilisticmodel, this is best done with maximum likelihood (ML). Suppose we aregiven n examples {t_(2D,i)}_(i=1) ^(n), the ML estimate for W and μ isobtained by minimizing: $\begin{matrix}{\sum\limits_{i = 1}^{n}\quad\left( {{\frac{1}{\sigma^{2}}{{t_{2D} - {f\quad\left( {T_{i}\left( u_{i} \right)} \right)}}}^{2}} + {u_{i}}^{2}} \right)} & (3)\end{matrix}$over all unknowns. The standard deviation σ is estimated a priori fromthe data. Once the model parameters W and μ have been learned fromexamples, they are kept fix. In practice, to minimize (3) wealternatively optimize over (W, μ) and {u_(i)}_(i=1) ^(n) using gradientdescent. Initial estimates can be obtained by intersecting 3D structurefrom each set of images and then applying PPCA algorithms for the linearpart. The normalization T_(i)(.) is chosen such that each normalized 3Dsample has zero mean and unit variance.

There are three different types of geometric features embedded in themodel.

Points: A 3D point which is visible in m>1 images will be represented inthe vector t with its 3D coordinates (X,Y,Z). For points visible in onlyone image, m=1, no depth information is available, and such points arerepresented similarly to apparent contour points.

Curves: A curve will be represented in the model by a number of pointsalong the curve. In the training of the model, it is important toparameterize each 3D curve such that each point on the curveapproximately corresponds to the same point on the corresponding curvein the other examples.

Apparent contours: As for curves, we sample the apparent contours (inthe images). However, there is no 3D information available for theapparent contours as they are view-dependent. A simple way is to treatpoints of the apparent contours as 3D points with a constant,approximate (but crude) depth estimate.

Finding Image Features

In the on-line event of a new input sample, we want to automaticallyfind the latent variables u and, in turn, compute estimates of the 3Dfeatures t. The missing component in the model is the relationshipbetween 2D image features and the underlying grey-level (or colour)values at these pixels. There are several ways of solving this, e.g.using an ASM (denoted the grey-level model) or detector basedapproaches.

The Grey-Level Model

Again, we adopt a linear model (PPCA). Using the same notation as in(1), but now with the subscript gl for grey-level, the model can bewrittent _(gl) =W _(gl) u _(gl)+μ_(gl)+ε_(gl)  (4)where t_(gl) is a vector containing the grey-level values of all the 2Dimage features and ε_(gl) is Gaussian noise in the measurements. In thetraining phase, each data sample of grey-levels is normalized bysubtracting the mean and scaling to unit variance. The ML-estimate ofW_(gl) and μ_(gl) is computed with the EM-algorithm [5].Detector-Based Methods

Image interest points and curves can be found by analyzing the imagegradient using e.g. the Harris corner-detector. Also, specially designedfilters can be used as detectors for image features. By designing thefilters so that the response for certain local image structures arehigh, image features can be found using a 2D convolution.

Classification Methods

Using classifiers such as SVM, image regions can be classified ascorresponding to a certain feature or not. By combining a series of suchclassifiers, one for each image feature (points, curves, contours etc.)and scanning the image at all appropriate scales the image features canbe extracted. Examples can be e.g. an eye detector for facial images.

Deformable Models

Using a deformable model such as the Active Contour Models, also calledsnakes, of a certain image feature is very common in the field of imagesegmentation. Usually the features are curves. The process is iterativeand tries to optimize an energy function. An initial curve is deformedgradually to the best fit according to an energy function that maycontain terms regulating the smoothness of the fit as well as otherproperties of the curve.

Surface Fitting to the 3D Data

Once the 3D data is recovered, a surface model can be fitted to the 3Dstructure. This might be desirable in case the two-step procedure aboveonly produces a sparse set of features in 3D space such as e.g. pointsand space curves. Even if these cues are characteristic for a particularsample (or individual), it is often not enough to infer a completesurface model, and in particular, this is difficult in the regions wherethe features are sparse. Therefore, a 3D surface model consisting of thecomplete mean surface is introduced. This will serve as adomain-specific, i.e. specific for a certain class of objects,regularizer. This approach requires that there is dense 3D shapeinformation available for some training examples in the training data ofthe object class obtained from e.g. laser scans or in the case ofmedical images from e.g. MRI or computer tomography. From these dense 3Dshapes, a model can be built separate from the feature model above. Thismeans that, given recovered 3D shape, in the form of points and curves,from the feature model, the best dense shape according to the recovered3D shape can be computed. This dense shape information can be used toimprove surface fitting.

To illustrate with an example, consider the case of the object classbeing faces. The model is then learned using e.g. points, curves andcontours in images together with the true 3D shape corresponding tothese features obtained from e.g. multi-view stereo techniques. A secondmodel is then created and learned using e.g. laser scans of faces,giving a set of face surfaces. This second model can be used to find themost probable (or at least highly probable) mean face surface (accordingto the second model) corresponding to the features or the recovered 3Dshape. A surface can then be fitted to the 3D shape with the additionalcondition that where there is no recovered 3D shape, the surface shouldresemble the most probable mean face surface.

As a second example, consider the case of the object class being aparticular blood vessel, e.g. the aorta. The model is then learned usinge.g. curves and contours in images together with the true 3D shapeobtained as e.g. a 3D MRI image. From the true 3D shapes a second modelis learned comprising of the surface of the aorta. Then the mostprobable (or highly probable) aorta surface can be recovered from theimage features or from the 3D shape recovered by the primary shapemodel.

The method provides the most probable or an at least highly probable 3Dshape, in many applications this is sufficient and the identificationand/or verification process is not necessary for the final application.

We have now described the underlying method used for verification and/oridentification purposes. Referring now to FIG. 3 a description of adevice 400 implementing the preferred method according to the presentinvention will be given. Such a device 400 may be any appropriate typeof computational device such as, but not limited to, a personal computer(PC), workstation, embedded computer, or stand alone device with acomputational unit 401, such as a microprocessor, DSP (digital signalprocessor), FPGA (field programmable gate array), or ASIC (applicationspecific integrated circuit). The device 400 has some input means 404for obtaining images for analysis and final identification and/orverification. The input means 404 may be of any suitable communicationinterface depending on image type and include, but is not limited to,USB (universal serial bus), frame grabber, Ethernet, or Firewire. Imagedata is transferred to a computational unit 401 wherein software forexecution of the above described method according to the presentinvention resides. The device 400 may further comprise some volatile ornon-volatile memory 402 containing information related to a referencematerial for comparison and/or analysis purposes, e.g. known 2D-3Drelationships of objects of interest. The device 400 may still furthercomprise communication means for communicating with other computationaldevices over e.g. a network protocol (such as Ethernet or similarprotocols) and output means 405 for outputting results to for instance ascreen for convenient viewing or to a control device (not shown) forcontrolling an external process wherein the objects of interest are partof. Such processes may include, but is not limited to, industrialproduction processes where objects may be selected or deselecteddepending on the result from the identification and/or verificationmethod according to the present invention, security processes again forselection or deselection purposes in for instance airport securitysystems for examination of the contents of suitcases, bags or otherluggage equipment, or medical applications where the recovered 3D shapemay be used e.g. for navigation of instruments or medical devices.

The method for object recognition according to the present invention maybe illustrated using FIG. 4. The method may comprise the followingsteps:

-   -   1. Obtaining at least one image of an object to be identified        and/or verified (501);    -   2. Detecting image features, such as curves, points, and        apparent contours (502).    -   3. Analysing the obtained image and inferring 3D shape        corresponding to the image features, using a statistical shape        model (503);    -   4. Comparing the analysis with reference images previously        obtained and comparing the 3D shape in a sparse or dense form        with reference 3D shape previously obtained (504); and    -   5. Responding to an output from the comparison process (505).

In another embodiment of the present invention a system is used forobtaining images, analyzing, and responding to results from theidentification and/or verification process, as may be seen in FIG. 5.Such a system may include at least one image acquisition device 601 orany other device or unit for obtaining a representation of the object607, a computational device 400, 603 as described above, and some typeof responsive equipment such as e.g. the industrial process equipment orthe security process equipment described above. At least one imageacquisition device 601 is used for acquiring one or more images (or 2Drepresentation) which are transferred 602 to the computational device603 for analysis and verification and/or identification. The result fromthis process is transmitted to a control system or display system 604.In the case of a face detection system at least one image of a person isobtained, for instance the face of the person, and the image or imagesare transmitted to the computational device 603, using any suitablecommunication means 602 (wired or wireless), for analysis and comparisonof the acquired image or images with data obtained from referencemeasurements for example with known 2D-3D relationships; however,comparison may be made between an inferred 3D shape with a stored 3Dreference data or between a 2D surface model with a stored 2D referencesurface model. The result may be made available through for instance adisplay unit 604 and may for illustrative purposes be displayed withboth a reference image 605 and the obtained image 606 or images renderedfrom the recovered 3D shape as shown in FIG. 5. It should be appreciatedby the person skilled in the art that the image acquisition systemand/or display/control system may be incorporated with the computationaldevice forming an integral unit and that the result may be displayed inany suitable manner and is not limited to the above described example.Instead of transferring the result to a display unit 604 it may be usedin any suitable control process for controlling e.g. an alarm, anentrance system, control gate, toll gate, and so on.

Some of the benefits the present invention contributes to the technicalfield may be illustrated with the following list:

-   -   Any number of images, even as few as a single image, may be used        to automatically recover the 3D shape of an object in the object        class.    -   A statistical multi-view model that represents 2D and 3D data        consistently.    -   The process is automatic and computationally efficient.    -   The process is robust to illumination and specular reflections        which is a problem for 3D reconstruction methods based on image        correlation or photo-consistency.    -   Surfaces can be fitted to the 3D structure using domain specific        regularizers learned from statistical shape models.

The flexibility of the present invention may be illustrated with thefollowing list:

-   -   The statistical shape model may be used for any class of objects        and the projection of these objects in images.    -   The approach may be used for any kind of imaging device (camera,        X-ray, multi-spectral, thermal, etc.).    -   The invention may be used with any number of imaging devices        (one or more).    -   The invention includes the possibility of combining many        different techniques for establishing 2D to 3D correspondence        (image acquisition systems, range scanners, stereo image        systems, multi-view stereo image systems, X-ray etc.)    -   The invention includes the possibility of using different        techniques, such as ASM, gradient based methods or deformable        models, for finding the image features.    -   If the object class contains non-rigid objects, the invention        includes the possibility to establish 2D to 3D models for        different deformations of the object (e.g. different facial        expressions).    -   The invention includes the possibility of using a statistical        shape model for surface fitting to the recovered 3D shape.

The reference representations of objects may be stored in severaldifferent locations and with different types of systems, such as, butnot limited to, locally on some non-volatile memory in a deviceutilizing the object recognition according to the present invention, ina centralized server, e.g. a database server, or a personalidentification card containing a reference representation of an objectsuch as a person and this identification card may be used in forinstance an access system. Communication between an object recognitionsystem and a reference representation storage system may be utilizedwith different types of security levels and/or schemes, such as RADIUS,DIAMETER, SSL, SSH, or any other encrypted communication system asunderstood by the person skilled in the art.

Possible application areas for the above described invention range fromobject identification and verification in industrial processes,determining and/or identifying objects for security reasons, objectrecognition for military purposes, e.g. automatic determination ofmilitary vehicles, military ships, aircrafts, and so on, facerecognition systems for many different applications, e.g. biometrics,information security, law enforcement, smart cards, access control andso on.

The above mentioned and described embodiments are only given as examplesand should not be limiting to the present invention. Other solutions,uses, objectives, and functions within the scope of the invention asclaimed in the below described patent claims should be apparent for theperson skilled in the art.

1. A method for object recognition of a three dimensional (3D) object,comprising the steps of: obtaining at least one two dimensional (2D)representation of said object; detecting image features in said obtained2D representation; recovering a highly probable 3D shape of said objectof a certain object class consistent with 2D images of said object usingat least one obtained image where 2D features are detected and using alearned statistical multi-view shape model of the shape variation; andcomparing said recovered 3D shape with a reference representation of atleast one object of said object class.
 2. The method according to claim1, wherein said recovered 3D shape is a complete surface model.
 3. Themethod according to claim 2, wherein said complete surface model isinferred from 2D or 3D features.
 4. The method according to claim 1,wherein said object class contains non-rigid objects and saidstatistical shape model is learned using 2D and 3D data specific forpossible deformations of the objects in said non-rigid object class. 5.The method according to claim 1, further comprising the step ofidentifying an individual object of an object class or aiding in theidentification of an individual object using said recovered 3D shape. 6.The method according to claim 1, further comprising the step ofverifying the identity of an individual object of an object class oraiding in the verification of the identity of an individual object usingsaid recovered 3D shape.
 7. The method according to claim 2, furthercomprising the step of: fitting a surface to said recovered 3D shapeusing a learned statistical shape model for said surface of the objectin order to regularize said surface shape in a manner specific for saidobject class.
 8. The method according to claim 1, wherein said objectmay be one or several of: a human face, a human body, inner organ(s) ofa human body, blood vessel, animal, inner organs of an animal, a tumor,manufactured product(s) from an industrial process, a vehicle, anaircraft, a ship, military object(s).
 9. The method according to claim1, wherein said reference representation is stored in at least one of anon-volatile memory, database server, and personal identification card.10. A device for object recognition of a three dimensional (3D) object,comprising: means for obtaining at least one two dimensional (2D)representation of said object; means for detecting image features insaid obtained 2D representation; means for recovering a highly probable3D shape of said object of a certain object class consistent with 2Dimages of said object using one or more images where 2D features aredetected and using a learned statistical multi-view shape model of theshape variation; and means for comparing said recovered 3D shape with areference representation of at least one object of said object class.11. The device according to claim 10, wherein said recovered 3D shape isa complete surface model.
 12. The device according to claim 11, whereinsaid complete surface model is inferred from 2D or 3D features.
 13. Thedevice according to claim 10, wherein said object class containsnon-rigid objects and said statistical shape model is learned using 2Dand 3D data specific for possible deformations of the objects in saidnon-rigid object class.
 14. The device according to claim 10 furthercomprising means for identifying an individual object of an object classor aiding in the identification of an individual object using saidrecovered 3D shape.
 15. The device according to claim 10, furthercomprising means for verifying the identity of an individual object ofan object class or aiding in the verification of the identity of anindividual object using said recovered 3D shape.
 16. The deviceaccording to claim 11, further comprising means for: fitting a surfaceto said recovered 3D shape using a learned statistical shape model forsaid surface of the object in order to regularize said surface shape ina manner specific for said object class.
 17. The device according toclaim 10, wherein said object may be one or several of: a human face, ahuman body, inner organ(s) of a human body, blood vessel, animal, innerorgans of an animal, a tumor, manufactured product(s) from an industrialprocess, a vehicle, an aircraft, a ship, military object(s).
 18. Thedevice according to claim 17, wherein said recovered 3D shapes of bloodvessels or organs recovered from 2D projections, e.g. using X-rayimaging, are used for navigating steerable catheters or aidingphysicians by displaying said recovered 3D shape.
 19. The deviceaccording to claim 17, wherein said recovered 3D shapes of facialfeatures are used to identify or to verify an identity of an individualin an access control system or security system, resulting in anacceptance or rejection of said individual.
 20. The device according toclaim 10, further comprising an interface for communicating with apersonal identification card wherein said reference representation isstored.
 21. A computer program stored in a computer readable storagemedium and executed in a computational unit for object recognition of athree dimensional (3D) object, comprising: an instruction set forobtaining at least one externally acquired two dimensional (2D)representation of said 3D object; an instruction set for detecting imagefeatures in said obtained 2D representation; an instruction set forrecovering a highly probable 3D shape of said 3D object of a certainobject class consistent with 2D images of said 3D object using one ormore images where 2D features are detected and using a learnedstatistical multi-view shape model of the shape variation; and aninstruction set for comparing said recovered 3D shape with a referencerepresentation of at least one object of said object class;
 22. Thecomputer program according to claim 21, further comprising aninstruction set for identifying and/or verifying an individual object ofan object class or aiding in said identification and/or verification ofsaid individual object using said recovered 3D shape.
 23. A system forobject recognition of a three dimensional (3D) object, comprising: meansfor obtaining at least one two dimensional (2D) representation of said3D object; means for detecting image features in said obtained 2Drepresentation; means for recovering a highly probable 3D shape of said3D object of a certain object class consistent with 2D images of said 3Dobject using one or more images where 2D features are detected and usinga learned statistical multi-view shape model of the shape variation;means for comparing said recovered 3D shape with a referencerepresentation of at least one object of said object class; and meansfor responding to a result from said means for comparison.
 24. Thesystem according to claim 23, further comprising means for identifyingand/or verifying an individual object of an object class or aiding insaid identification and/or verification of said individual object usingsaid recovered 3D shape.
 25. The system according to claim 23, whereinsaid reference representation is stored in at least one of anon-volatile memory, database server, and personal identification card.